Add monospace fallback font.

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Change-Id: I93b0c59fbfcb759b4b5b19daa5e167c7ad8b97c7
Reviewed-on: https://bazel-review.googlesource.com/c/5651
MOS_MIGRATED_REVID=131431041
diff --git a/site/_sass/style.scss b/site/_sass/style.scss
index b1ebf95..e8ce593 100644
--- a/site/_sass/style.scss
+++ b/site/_sass/style.scss
@@ -1,6 +1,6 @@
 $body-font-family: 'RobotoDraft', 'Helvetica Neue', Helvetica, Arial,
                    sans-serif;
-$code-font-family: 'Source Code Pro';
+$code-font-family: 'Source Code Pro', monospace;
 
 $link-color: #4caf50;
 $link-hover-color: darken($link-color, 10%);